The invention relates to a device for printing a print carrier in a printing region using a stationary ink-jet printing head and with a print carrier moved downstream in the Z-direction of the printing region. The invention is employed in fully electronic digital printing devices in which recording carriers have variable dimensions (i.e. thickness and size). It is particularly suitable for use in voucher printers, franking machines, addressing machines and other mail processing appliances with a transport and printing device for mail items.
German Patent DE 25 01 035 C2 discloses a printing drum with a single ink-jet printing head. The printing drum has a transport function and a printing function, and therefore the ink-jet printing head cannot print the entire printing region. Variable information can be printed only by the ink-jet printing head. Regions in which the printing information cannot, in principle, be changed therefore remain in the printing image.
Modern franking machines, such as, for example, the thermotransfer franking machine known from U.S. Pat. No. 4,746,234, employ fully electronic digital printing devices. It is consequently possible, in principle, to print any desired texts, codes and special characters in the franking-stamp printing region and any desired advertising block print or one assigned to a cost center. A franking machine, for example T1000 from the applicant Francotyp-Postalia AG and Co., is controlled by a microprocessor control surrounded by a secured housing which has an orifice for feeding a letter. Whenever a letter is fed, a mechanical letter sensor (microswitch) transmits a print demand signal to the microprocessor which generates a printing image and, after billing the mailing value to be franked, triggers printing. The franking imprint contains previously entered and stored mail information for transporting the letter.
U.S. Pat. No. 5,467,709 discloses a printing device for an ink-jet franking machine, a franking print being printed onto a mail item by an ink-jet printing head during approximately horizontal letter transport. For printing, the ink-jet printing head is disposed in a stationary manner in a recess behind a guide plate. A rotating transport belt serves as a transport device and is likewise disposed at the side of the guide plate. A back-pressure device with a plurality of rollers is disposed on the other side, opposite the guide plate, so that a fed mail item is clamped between the rollers of the back-pressure device and the rotating transport belt. However, the configuration cannot prevent the print carriers from running askew. Even an insufficiently tensioned transport belt or a not exactly parallel alignment of the axes of those rollers on which the transport belt rotates gives rise to the above-mentioned risk. Due to the multiplicity of rollers of the back-pressure device, the latter is dynamically redundant.
German Patent DE 196 05 015 C1, corresponding to U.S. Pat. No. 5,949,444, has already proposed a version of a printing device of a JETMAIL ink-jet franking machine of the applicant Francotyp-Postalia AG and Co., which, in the case of nonhorizontal approximately vertical letter transport, executes a franking print by an ink-jet printing head which is disposed in a stationary manner in a recess behind a guide plate. A rotating transport belt serves as a transport device, with pressure elements for the mail items (letters with a thickness of up to 20 mm, DIN B4 format) or for franking strips that are configured to be capable of being glued onto packets of any thickness. The print carrier (letter, packet, franking strip) is clamped between the pressure element and the guide plate.
The transport and printing device is disposed in the base and is controlled by a meter. A trigger sensor for the printing process is disposed in the base, just in front of the ink-jet printing head recess, for detecting the start of a letter and cooperates with an incremental generator on the drive of the transport belt. By use of a transmitted-light barrier as a trigger sensor (Published, European Patent Application EP 0 901 108 A2), the leading edge of even especially thick mail items is detected unequivocally. Moreover, optical sensors for detecting the build-up of mail items are employed in the base of the JETMAIL. An automatic feed and a dynamic balance are disposed in the CONDORD franking system upstream of the JETMAIL franking machine, thus allowing genuine mixed-mail processing for mail items of widely differing formats, thicknesses and weights. At very high printing speeds, it becomes increasingly more difficult to print a stamping print of relatively high quality that allows mechanical evaluation with a high degree of reliability. A rotating transport belt should therefore have no stretching, even under mechanical and thermal load, and the pressure elements should not allow any slip during the transport of the mail items. Only transport and printing devices that are of complicated constructions and are cost-intensive have hitherto satisfied these requirements.
There have also already been proposed more simply constructed transport and drive devices without back-pressure device (German Patent DE 196 05 014 C1) or with a back-pressure device (International Patent Disclosure WO 99/44174) in the vicinity of the printing region of at least one ink-jet printing head. In International Patent Disclosure WO 99/44174, the latter is disposed downstream of a pair of draw-in rollers in the transport direction, the upper roller being driven and the lower back-pressure roller being sprung. A further pair of rollers downstream of the ink-jet printing head, near the ejection, likewise exerts a force on the print carrier. The printing region is at a distance from the force transmission region of one of the pairs of rollers of more than one radius of the respectively driven roller. Although, in principle, the printing information can be changed in all regions as a result of digital printing, the print is nevertheless of lower quality, the higher the selected transport speed. In particular, when two ink-jet printing heads are employed, an offset may occur in the printing image (correspondence error) along a printing length in the transport direction, thus making the mechanical evaluation of the printing image more difficult. The force action of the further pair of rollers downstream of the ink-jet printing head, near the ejection, leads to a different path length and therefore, in the case of two ink-jet printing heads offset to one another, to the correspondence error in the printing image. The print quality demanded within the framework of current programs of the mail service providers, for example the information-based Indicia program of the USPS, could therefore be achieved only at the expense of a low printing speed. Another disadvantage is the small thickness of the print carriers that can be printed by such a simply constructed printing device.
It is accordingly an object of the invention to provide a device for printing a print carrier which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which makes it possible, even at very high printing speeds, to have a print of higher quality. Printing is to take place directly onto print carriers that have a thickness of up to 10 mm.
With the foregoing and other objects in view there is provided, in accordance with the invention, a printing device containing a driven transport drum and a non-driven back-pressure device resilient in a Y-direction and disposed opposite the driven transport drum. The driven transport drum and the non-driven back-pressure device define a force transmission region there-between and exert a transport force on a print carrier in the force transmission region. An ink-jet printing head is disposed axially relative to the driven transport drum in an X-direction. The print carrier is printed on in a printing region by the ink-jet printing head and the print carrier is moved downstream in a Z-direction in the printing region. The printing region is at a distance from the force transmission region, and the X-direction is orthogonal to the Z-direction and orthogonal to the Y-direction.
A rotating transport drum serves as the transport device and is disposed on the same side of the guide plate as the ink-jet printing head. The resilient back-pressure device is disposed on the other side, opposite the transport drum, so that a fed print carrier (i.e. letter) is clamped between the transport drum and the back-pressure roller of the back-pressure device. The clamping location is referred to hereafter as the force transmission region, because the force for transporting in the transport direction is transmitted to the print carrier there. None of the back-pressure rollers of the back-pressure device is disposed opposite the ink-jet printing head. The ink-jet printing head is at a distance, or the one hand, from the transport drum in the axial direction and, on the other hand, from the contact surface between the guide plate and print carrier, both distances being minimized. The printing region is offset relative to the force transmission region in the X-direction and is located at the edge of the printing drum. For printing, the at least one ink-jet printing head is disposed in a stationary manner behind a guide plate in a recess which starts at the edge of the printing drum. The imprint is applied contactlessly to the print carrier in the printing region during the transport of the print carrier in the Z-direction. The printing device may be configured for approximately horizontal, inclined or vertical transport of the print carrier in the Z-direction. For example, in a franking machine with the at least one ink-jet printing head, a franking print of high print quality is printed onto a moved mail item in the printing region. Although the transport drum is very large, so that even relatively thick mail items are properly picked up and transported, in the device according to the invention the furthest pixel of the printing region is nevertheless nearer to the force transmission region than corresponds to the radius of the transport drum.
The device for printing a print carrier in the printing region makes use, in the force transmission region, of a driven transport drum and non-driven back-pressure rollers or, alternatively, a non-driven back-pressure conveyor belt of the back-pressure device.
In accordance with an added feature of the invention, the driven transport drum has an edge and a radius of a circumference. And a distance of a furthest pixel in the printing region from the edge of the driven transport drum is smaller than the radius of the circumference of the driven transport drum.
In accordance with an additional feature of the invention, a housing having a slit-shaped orifice formed therein is provided. The driven transport drum and the non-driven back-pressure device are disposed in the housing. The driven transport drum and the back-pressure device exert the transport force on the print carrier in an area of the slit-shaped orifice of the housing. The slit-shaped orifice has a depth extending in the X-direction orthogonally to the Z-direction for the print carrier moved downstream, so that the force transmission region and the printing region are disposed within the slit-shaped orifice. The driven transport drum has a bearing axle running parallel to the X-direction and has an orifice formed therein. The ink-jet printing head has nozzles and an ink container disposed in the X-direction with the ink container at least partially in the orifice of the driven transport drum in such a way that the nozzles are located at the edge of the driven transport drum for emitting ink drops on demand, opposite to the Y-direction, onto a surface of the print carrier in the printing region. And the non-driven resilient back-pressure device exerts a spring pressure in the Y-direction.
In accordance with another feature of the invention, the non-driven back-pressure device has non-driven back-pressure rollers functioning as resilient devices.
In accordance with a further feature of the invention, the non-driven back-pressure device has at least one non-driven back-pressure conveyor belt functioning as a resilient device.
In accordance with a further added feature of the invention, a motor is disposed in the housing. A guide plate against which the print carrier rests and has a guide plate orifice formed therein is disposed on one side of the slit-shaped orifice of the housing. The driven transport drum exerts the transport force on the print carrier in a transport direction through the guide plate orifice in the guide plate when the motor is activated. A feed deck is disposed opposite the guide plate, on another side of the slit-shaped orifice of the housing. The feed deck has feed deck orifices formed therein for receiving the resilient devices of the non-driven back-pressure device. The feed deck orifices include a first orifice and a second orifice and the guide plate orifice and the first orifice of the feed deck are located opposite one another.
In accordance with another added feature of the invention, the guide plate has a further guide plate orifice formed therein for ink-jet printing from the nozzles of the ink-jet printing head. The further guide plate office is disposed next to the guide plate orifice so as to be offset in the X-direction.
The further guide plate orifice has a size corresponding to the printing region.
In accordance with further additional feature of the invention, a driven draw-in roller is provided. The guide plate has a further guide plate orifice formed therein for receiving the driven draw-in roller, and the further guide plate orifice is disposed next to the guide plate orifice. The guide plate orifice for the driven transport drum is offset to the further guide plate orifice in the Z-direction.
In accordance with another additional feature of the invention, a non-driven draw-in roller is disposed in the second orifice of the feed deck. The first orifice and the second orifice of the feed deck are disposed next to one another such that the first orifice is offset to the second orifice in the Z-direction.
In accordance with an added feature of the invention, the guide plate has a further guide plate orifice formed therein for detecting the print carrier and is disposed next to the guide plate orifice for the driven transport drum. The guide plate orifice is offset to the further guide plate orifice in the Z-direction.
In accordance with an additional feature of the invention, the second orifice of the feed deck is provided for detecting the print carrier and is disposed next to the first orifice of the feed deck such that the first orifice is offset to the second orifice in the Z-direction.
In accordance with another feature of the invention, the non-driven back-pressure device has a first fixed bearing axle, a resilent rocker mounted pivotably about the first fixed bearing axle, a first axle fastened on the resilent rocker, and a first tension spring acting on the resilent rocker. The non-driven back-pressure rollers are mounted rotatably on the first axle and act on the print carrier through the first orifice in the feed deck by a spring force of the first tension spring.
In accordance with a further feature of the invention, a pilot control mechanism having a front and disposed upstream of the non-driven back-pressure device is provided. The pilot control mechanism has a second fixed bearing axle, a sprung rocker disposed at the front along the transport path and is mounted pivotably about the second fixed bearing axle, a second axle fastened to the sprung rocker, a second tension spring acting on the sprung rocker, and a non-driven draw-in roller mounted rotatably on the second axle. An upper draw-in roller is disposed above the non-driven draw-in roller and the non-driven draw-in roller acts the upper draw-in roller or on the print carrier through the second orifice in the feed deck by a spring force of the second tension spring. A lifting rod is provided for coupling the sprung rocker to the resilent rocker in such a way that a movement of the sprung rocker caused by a thickness of the print carrier is transmitted at least partially to the resilent rocker being a rear rocker.
In accordance with a further added feature of the invention, the first tension spring has a spring constant being substantially higher than that of the second tension spring.
In accordance with a further additional feature of the invention, the sprung rocker and the resilent rocker are each formed of two angle levers including a first angle lever and a second angle lever each having legs including a first leg and a second leg. The sprung rocker and the resilent rocker each have a first spacer piece connected between the first leg of the two angle levers, a second spacer piece connected between the first leg and the second leg of each of the two angle levers, and a bolt fastened to the second leg of the first angle lever and the second leg of the second angle lever for spring suspension.
In accordance with another added feature of the invention, the lifting rod has a first hole and a second hole formed therein at opposite ends of the lifting rod. The sprung rocker has a further bolt disposed along the transport path and is held in the first hole at one end of the lifting rod. The bolt of the rear rocker is disposed along the transport path and is held in the second hole at the other end of the lifting rod.
In accordance with an added feature of the invention, the non-driven back-pressure device has a sprung long rocker, first axles fastened on the sprung long rocker, and supporting rollers mounted rotatably on the first axles. The non-driven back-pressure conveyor belt runs on tile supporting rollers. The non-driven back pressure device has second axles fastened on the sprung long rocker and deflecting rollers for the non-driven back-pressure conveyor belt are mounted rotatably on second axles. The non-driven back pressure device has a sprung short rocker, a third axle fastened on the sprung short rocker, and a non-driven lower draw-in roller mounted rotatably on the third axle. The non-driven back pressure device has a common fixed bearing axle and the sprung long rocker and the sprung short rocker are mounted pivotably about the common fixed bearing axle. The non-driven back pressure device has a feed deck with a first orifice and a second orifice formed therein, a first compression spring and a second compression spring. The non-driven back-pressure conveyor belt acts on the print carrier through the first orifice in the feed deck by a spring force of the first compression spring, and the non-driven lower draw-in roller acting on the print carrier through the second orifice in the feed deck by a spring force of the second compression spring.
In accordance with an additional feature of the invention, the first compression spring has a spring constant substantially higher than that of the second compression spring.
In accordance with another feature of the invention, the locking nuts fasten the second axles to the sprung long rocker.
In accordance with a further feature of the invention, at least one friction covering rests annularly against a circumference of the driven transport drum.
In accordance with another added feature of the invention, the driven transport drum has a bearing axle. A worm wheel, a drive belt, and a driving wheel driven by the drive belt are disposed near one end face of the driven transport drum on the bearing axle of the driven transport drum. A motor driving the driven transport drum is provided. The motor has a motor axle and a worm pinion disposed on the motor axle and engages the worm wheel. A driven wheel and an upper draw-in roller coupled to the driven wheel which is driven by the drive belt, are provided.
In accordance with yet another feature of the invention, the driving wheel and the driven wheel are toothed-belt wheels, and the drive belt is a toothed belt.
In accordance with a further feature of the invention, an encoder disk, which can be sensed by a light barrier in an encoder, is disposed on the motor axle.
In accordance with a concomitant feature of the invention, the driven transport drum has an end face with markings disposed on the end face, near a circumference of the driven transport drum to be read by an encoder.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for printing a print carrier, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.